The Mini-RF team is acquiring bistatic radar measurements of the lunar surface to understand the scattering properties of materials as a function of bistatic angle. These observations have produced the first lunar bistatic radar images ever collected with non-zero phase angles. The goal of these observations is to test the hypothesis that some permanently shadowed areas near the lunar poles contain water ice.
The bistatic phase angle is the angle between the transmitted and received beam, and is determined by the positions & orientations of the radar transmitter and receiver. For radar observations that use the same antenna to transmit and receive a signal (e.g. normal SAR observation from orbit), the bistatic angle is zero, and the data are referred to as monostatic. NASA’s Mini-RF on the Lunar Reconnaissance Orbiter and the Arecibo Observatory in Puerto Rico are operating in a bistatic mode. Arecibo transmits a signal which is reflected off the lunar surface, and received by Mini-RF in orbit..
Mini-RF receives orthogonal linear polarizations as well as their relative phase. This architecture is equivalent to the hybrid dual-polarimetric architecture of the monostatic mode for the Mini-RF instrument and, therefore, allows for the calculation of the Stokes parameters (S1, S2, S3, S4) that characterize the backscattered signal (and the products derived from those parameters).
To investigate whether certain polar craters contain ice deposits Mini-RF is acquiring data from a range of targets. In addition to polar anomalous craters, we are imaging non-polar targets that have high monostatic CPR values, typically ejecta blankets from relatively fresh craters. We acquire these data at a variety of bistatic angles. The goal is to characterize how CPR varies as a function of bistatic angle for craters deposits in which the presence of water ice is not expected. This is expected to be different from how CPR varies for icy deposits. Here we report on our initial results from these observations.